As a result of the energy crisis the trend toward the development of higher efficiency heating appliances has accelerated. This trend was further facilitated by a growing concern with the environment with its emphasis on reducing the use of natural resources. The resulting greater concern for energy efficiency both in furnaces, water heaters and home insulation resulted in major improvements in home energy efficiency. The push toward greater efficiency also had effects on construction techniques and design choices.
One important energy saving construction technique was reducing air infiltration into and out of a building. So-called tight construction requires appliances that require no aspiration or which ventilate directly to the outside. This led to the installation of many electric water heaters and electric heat-pumps.
Builders immediately took advantage of the appliances and construction techniques to reduce construction costs by eliminating chimneys in new construction. Although electric water heaters and heat-pumps do not require a chimney because they do not produce exhaust gases, they are typically more costly to operate than a gas or oil fired water heater.
So called "direct vent" gas fired water heaters were developed and used to replace the electric water heaters in homes built without chimneys. However the typical direct vent water heater uses a fan that draws air from the home to dilute the exhaust gases so they are sufficiently low in temperature to be exhausted without a chimney. In a modern tightly constructed home drawing air from the home both for combustion and for dilution presents a supply problem in obtaining sufficient makeup air.
Another type of water heater, exemplified in U.S. Pat. Nos. 5,020,512 and 3,707,142, brings makeup air to the water heater from outside, through an annulus around the exhaust pipe. This coaxial duct arrangement has two benefits. First, the inner exhaust pipe is cooled and insulated allowing it to penetrate the wall of a house without necessitating a chimney. Secondly the makeup air for combustion is supplied from the building exterior at the same pressure at which the exhaust pipe discharges. This type of water heater relies on natural draft to control the circulation of air. Use of natural draft limits the placement of the unit within a building and requires standard exhaust components to assure functioning of the natural draft.
In many parts of this country and other countries natural gas is not available and heating oil is the preferred fuel for home and water heating. High quality oil fired water heaters have realized extended installed lives with only routine maintenance. This type of water heater has, particularly in the market for oil fired water heaters, established a market requirement for extreme durability.
What is needed is an oil fired water heater which can be installed in a home without a chimney.